Rubber-based nanocomposites prepared by solid-phase mixing with precipitated silica nanoparticles are typically stronglyaggregated systems with different levels of spatial organization, as highlighted by our group in the past [1]. The strategythat we developed these past years was to investigate such systems based on the study of simplified industrial sampleswith ingredients limited to a strict minimum. The analysis of small-angle X-ray scattering data can then be performed onthe scale of a micrometric simulation box. Tens of thousands of “model” nanoparticles are embedded in the matrix, andtheir dispersion strongly affects both the mechanical properties of the material, and the scattered intensity. A statisticalmethod based on a reverse Monte Carlo solution of this many-parameter scattering problem will be presented, showingthat some key features like percolation can be described [2].Another key feature of rubber nanocomposites refers to the influence of the filler surfaces on the polymer structure anddynamics, and some recent progress will be discussed [3]. In particular, we have studied blends of short and long chains,where one chain type is deuterated, by small-angle neutron scattering. Different degrees of spatial segregation could beidentified recently, including a peculiar, “fish-shaped” interfacial gradient characterized also by reverse Monte Carlosimulations, this time of the interface.[1] Guilhem P. Baeza, Anne-Caroline Genix, C. Degrandcourt, Laurent Petitjean, Jérémie Gummel, Marc Couty, Julian Oberdisse, Macromolecules 2013, 46, 317−329(cover article)[2] Musino D, Genix A-C, Chauveau E, Bizien T, Oberdisse J, Nanoscale 2020, 12:3907.[3] A.C. Genix, V. Bocharova, B. Carroll, P. Dieudonné-George, M. Sztucki, R. Schweins, A. P. Sokolov, and Julian Oberdisse, ACS Applied Materials and Interfaces,2021, in press

Rubber-based nanocomposites prepared by solid-phase mixing with precipitated silica nanoparticles are typically strongly aggregated systems with different levels of spatial organization, as highlighted by our group in the past [1]. The strategy that we developed these past years was to investigate such systems based on the study of simplified industrial samples with ingredients limited to a strict minimum. The analysis of small-angle X-ray scattering data can then be performed on the scale of a micrometric simulation box. Tens of thousands of “model” nanoparticles are embedded in the matrix, and their dispersion strongly affects both the mechanical properties of the material, and the scattered intensity. A statistical method based on a reverse Monte Carlo solution of this many-parameter scattering problem will be presented, showing that some key features like percolation can be described [2].Another key feature of rubber nanocomposites refers to the influence of the filler surfaces on the polymer structure and dynamics, and some recent progress will be discussed [3]. In particular, we have studied blends of short and long chains, where one chain type is deuterated, by small-angle neutron scattering. Different degrees of spatial segregation could be identified recently, including a peculiar, “fish-shaped” interfacial gradient characterized also by reverse Monte Carlo simulations, this time of the interface.References[1] Guilhem P. Baeza, Anne-Caroline Genix, C. Degrandcourt, Laurent Petitjean, Jérémie Gummel, Marc Couty, Julian Oberdisse, Macromolecules 2013, 46, 317−329 (cover article)[2] Musino D, Genix A-C, Chauveau E, Bizien T, Oberdisse J, Nanoscale 2020, 12:3907.[3] A.C. Genix, V. Bocharova, B. Carroll, P. Dieudonné-George, M. Sztucki, R. Schweins, A. P. Sokolov, and Julian Oberdisse, ACS Applied Materials and Interfaces, 2021, in press

Herein, we demonstrate that tuning of structural parameters and material chemistry enables control of the permeability and selectivity of gases (CO2, He, and CH4) in membranes based on poly(butyl methacrylate)-grafted nanoparticles (PGNs). Our data show that the presence of nanoparticles and the overall dense packing of grafted chains noticeable in PGNs with low grafting density have an adverse effect on the diffusivity of gases. This effect is compensated by an improvement in the solubility of CO2 gas promoted by the silica nanoparticle surface, yielding a substantial improvement in the permeability of CO2 versus CH4. In membranes with high grafting density, changes in the structural arrangements and alterations in the membrane porosity, evident from small-angle X-ray scattering and positron annihilation lifetime spectroscopy, positively influence the permeability of He and CO2 gases. In contrast, CH4 permeability in the same membranes is significantly suppressed, suggesting the formation of a unique, highly selective environment for gas separation. As a result, an improvement of up to 50% in selectivity for gas pairs containing large CH4 molecules is observed. Our studies provide fundamental insights into the role that structural parameters play in gas transport through polymer membranes, laying a foundation for the rational design of membranes with improved permeability and selectivity.

Rubber-based nanocomposites prepared by solid-phase mixing with precipitated silica nanoparticlesare typically strongly aggregated systems with different levels of spatial organization. The strategy thatwe developed several years ago to investigate such systems is based on the study of simplifiedindustrial samples with ingredients limited to a strict minimum. On the scale of a micrometricsimulation box, tens of thousands of nanoparticles are embedded in the matrix, and their dispersionstrongly affects the mechanical properties of the material – and which is reflected in the scatteredintensity. A statistical method based on a reverse Monte Carlo solution of this many-parameterproblem will be presented, showing that some key features like percolation can be described. [1]Another key feature of rubber nanocomposites refers to the influence of the filler surfaces on thepolymer dynamics, and some recent progress – including incoherent neutron spin-echo measurements– will be discussed. [2] Such results may be confronted to dielectric spectroscopy measurements whichin some cases are not conclusive due the impossibility to correctly resolve the α-relaxation in presenceof strong interfacial polarization processes. An original application of dielectric spectroscopy with asurprising measurement of the adsorption isotherm of coating agents onto silica buried in the polymermatrix will also be discussed. [3][1] Musino D, Genix A-C, Chauveau E, Bizien T, Oberdisse J, Nanoscale 2020, 12:3907.[2] Musino D, Oberdisse J, Farago B, Alegria A, Genix A-C, ACS Macro Letters 2020, 9:910.[3] Musino D, Oberdisse J, Sztucki M, Alegria A, Genix A-C, Macromolecules 2020, 53:8083.

Polymerized ionic liquids (PolyILs) are an emerging class of polymer electrolytes which offer solutions to many problems in current battery technology. They combine the attractive features of ionic liquids with the mechanical strength of polymeric materials. However, a major obstacle in use of dry PolyILs is their low ionic conductivity at ambient temperature, which remains below the level required for many applications (ca. 10-3 S/cm). In this context, it has been shown that a significant enhancement of the ionic conductivity can be obtained by decoupling the ion motion from the segmental dynamics in polymers. We will review recent results obtained in this field using broadband dielectric spectroscopy, and discuss the microscopic parameters controlling ionic conductivity in PolyILs below Tg [1]. In particular, our detailed study of imidazolium-based PolyILs helped to unravel the interplay between nanostructure and ion conduction mechanism [2]. We also report first quasi-elastic neutron scattering experiments in these polymers suggesting the role of fast dynamics in assisting ion transport in the glassy state [3].[1] V. Bocharova and A.P. Sokolov, Macromolecules 2020, 53, 4141.[2] B. Doughty, A.C. Genix, I. Popov, B. Li, S. Zhao, T. Saito, D. Lutterman, R. Sacci, B.G. Sumpter, Z. Wojnarowska, V. Bocharova, Phys. Chem. Chem. Phys. 2019, 21, 14775.[3] V. Bocharova, A.C. Genix, A. Kisliuk, G. Sala, N.C. Osti, E. Mamontov, A. P. Sokolov, J. Phys. Chem. B 2020, 124, 10539.

Polymer nanocomposites (PNCs) are made by the dispersion of hard fillers in a polymer matrix, where the fillers are usually added to enhance mechanical properties. Such materials attract industrial interest and their investigation is essential for the improvement of their performances. The latter are strongly related to the structural properties of PNCs: the dispersion state of nanoparticles (NPs) in the polymer melt is governed by the mixing protocols (e.g., solid phase mixing or solvent casting) and thermodynamics of the system (i.e., particle miscibility) which influence both filler-filler and filler-polymer interactions.The present study concerns nanocomposites obtained using hydrophilic silica NPs dispersed in two different polymer matrices: 1) poly(2-vinylpyridine) forming attractive NP/polymer interfaces or 2) a weakly interacting styrene-butadiene (SB) rubber. In the first system, the dynamical properties of the interfacial layer surrounding NPs are obtained using broadband dielectric spectroscopy (BDS). Moreover, we propose an original approach combining small-angle scattering experiments of X-rays and neutrons and simulations to investigate the static properties. Only in ideally well-dispersed systems using pre-adsorption of the polymer chains, a static interfacial layer with a gradient of density extending over a thickness of ca. 2 nm is evidenced based on the analysis with a form-free density profile. This gradient is found to be generated by out-of-equilibrium packing and folding of the preadsorbed layer.In the second polydisperse and disordered SB system, we recently proposed a reverse Monte-Carlo analysis of the scattering data giving access to NP aggregate mass distributions. In opposition to the previous system, BDS experiments are not conclusive regarding the impact of the industrial filler on the segmental relaxation. Therefore, we used neutron spin-echo spectroscopy (NSE) and demonstrate – here for the first time – that incoherent NSE based on fully hydrogenated compounds can be used to resolve small modifications of the segmental dynamics of PNCs.

Polymers with dynamic (transient) bonds, often called associating polymers, have been attracting significant attention in recent years due to their unique viscoelastic properties, self-healing ability, and recyclability. Nevertheless, understanding the mechanisms and the factors controlling their macroscopic properties remains limited due to the higher complexity introduced by the dynamic bonds. In this study, small-angle X-ray scattering (SAXS), broadband dielectric spectroscopy (BDS), and rheology were applied to unravel the structure and dynamics of telechelic associating polymers with different molecular weights. SAXS measurements revealed phase separation of the functional end groups with an average cluster size of ∼2–3 nm and the distance between clusters controlled by the chain length. Borrowing the interfacial layer model analysis of BDS data from the polymer nanocomposite field, we demonstrated the presence of an interfacial polymer layer with a thickness of ∼0.7–0.9 nm surrounding these clusters. Rheological measurements showed quantitatively that the presence of the interfacial layer significantly alters the viscoelastic behavior of these materials, indicating the crucial role of the interfacial layer in defining the macroscopic mechanical properties of the studied telechelic materials. The presented results emphasize that phase separation of the functional groups in associating polymers leads to very significant changes of the viscoelastic properties, opening a promising avenue in the design of novel functional materials.